1. Field of the Invention
The present invention relates to an improvement to a four-cycle engine lubrication structure.
2. Description of Related Art
Four-cycle engine lubrication structures such as, for example, the "Four-cycle Engine Lubrication Apparatus" of Japanese Patent Publication No. Hei. 6-25527 are well known.
The above technology relates to a four-cycle engine lubrication apparatus capable of preventing drops in output accompanying engine oil agitation and capable of reliably providing oil to each of the necessary places within the engine even when the vehicle is at an incline. As shown in FIG. 2 of the above publication, there is provided a crank chamber 12, a transmission chamber 13 separated from the crank chamber 12 by a bulkhead 14, a through hole 15 provided at the bulkhead 14 to allow the crank chamber 12 and the transmission chamber 13 to communicate, and a unidirectional valve 16 provided at the through hole 15 for allowing oil to flow only from the crank chamber 12 to the transmission chamber 13.
In the above technology, when the pressure within the crank chamber 12 becomes high, the unidirectional valve 16 opens and oil within the crank chamber 12 flows through the through hole 15 to the transmission chamber 13. However, oil is collected at a position higher than the through hole 15 within the transmission chamber and this may hinder opening of the valve 16. Therefore, the oil does not move smoothly from the crank chamber 12 to the transmission chamber 13.
There is also an problem in the above technology, since air becomes mixed with the oil within the crank chamber 12. Therefore, when the oil flows into the transmission chamber 13, air is mixed in with the oil within the transmission chamber 13 and the oil is oxidized, causing increased deterioration of the oil.